Patent GB-885070-A (GB)
Title: Improvements in or relating to apparatus for flash-butt welding
Inventor: YOUNG WILLIAM FORBES
IPC: B23K11/04
Filed: 1959-06-01
Abstract: 885,070. Welding by pressure. RESISTANCE WELDERS Ltd. May 11, 1960 [June 1, 1959; Oct. 2, 1959], Nos. 18660/59 and 35541/59. Class 83 (4). Apparatus for flash-butt welding comprises a pair of work supporting platens, liquid pressure means to effect relative movement of the platens, valve means controlling the direction of the thrust exerted by the liquid pressure means and means to control the position of the valve means including two opposing forces acting simultaneously on the valve means so that the relative magnitude of the forces controls the position of the valve means, at least one of the forces varying with the instantaneous value of the current or voltage existing during flashing. The welding transformer 17 is connected to the fixed and movable platens 11, 12 and the platen 12 carries a ram 19 in a cylinder 21 supplied with liquid at its forward end via a pipe 28 and at its rear end via a pipe 35. The pipe 35 is connected through an intensifier valve 27 to a valve 25, the slide of which controls whether the rear end of the ram is connected to a pump 23 drawing from a reservoir 22 or to the reservoir. The pipe 28 is connected to the pump and a branch 29 is connected to the valve. The slide of the valve normally covers a port to which the conduit 29 is connected and a port to which a conduit 31 leading to the reservoir is connected, movement of the slide to the left connecting the back of the cylinder 21 with the pump and movement to the right connecting the cylinder with the reservoir. Acting on armatures at opposite ends of the slide are solenoids 43, 44, the solenoid 43 being fed through a rectifier from a voltage pick-up 59 across the workpieces and solenoid 44 being fed through a rectifier either to a coil 58 surrounding the transformer lead to the fixed platen or to the secondary of a transformer fed from a separate supply. In operation with the solenoid 44 initially connected to the transformer secondary the slide of valve 25 is moved to the right to allow the pump to supply only the left-hand side of the cylinder 21 to open the platens. With workpieces on the platens the solenoid 44 is connected to the coil 58 and the alternating supply is connected across the workpieces. The voltage is picked up by 59 causing current to flow in solenoid 43 which pulls the valve slide to the left-no current yet flowing in solenoid 44-to allow the pump to supply the right-hand end-of the cylinder 21 to move the workpieces into contact. Flashing commences and current in solenoid 44 tends to return the valve 25 to the right and voltage drop across the workpieces causes solenoid 43 to decrease its pull to the left. The pieces burn away and continue to approach and at a predetermined spacing of the pieces the valve 25 will assume its neutral position, any change in the voltage/current ratio moving the plate 12 in one direction or the other. As the pieces burn away the platen 12 moves forward until a cam 54 carried by the platen opens a switch 52 to cut-off the flashing current and a cam 53 closes a switch 51 to energize a solenoid 48 causing the intensifier piston 36 to move upwardly, thus butting the workpieces together. In a modification, the pressure in both ends of the cylinder 21 is controlled and in either case one of the solenoids 43, 44 may be connected to a constant voltage source. In a further modification the valve slide is moved in one direction by a spring and in the other by a current or voltage energized solenoid. The valve slide may be controlled by a pilot valve acted on by the voltage pick-up and current solenoids.